The production and manufacture of semiconductors is a complex and meticulous process. One area in which particular care and precision are required is the heating in furnaces for vapor deposition, diffusion and other processes. Specific areas of concern are particulate count and the alignment of the silicon wafers in the process tubes of the furnace.
In the existing systems, friction is created between the wafer sled or boat and the inner surface of the process tube. This friction causes multiple problems. The most significant problem is that the friction creates quartz dust which then increases the particulate count at the diffusion stage. Since the wafer's characteristics are directly related to their purity, attaining a lower particulate count will directly improve the quality of the wafer specifications. If the level of dust from friction is high, then the wafers will be contaminated and the yield will drop dramatically. Additional problems incurred include more time being required for cleaning the process tube and therefore a decrease in production capability, downtime of the furnace is increased and wear on the tubes is increased.
The presently existing retraction systems use two rods lying in a horizontal plane to support the carriage which in turn holds the paddle containing the wafers. All of the supporting mechanism and therefore, the adjusting mechanism, is underneath the paddle. Adjustments are therefore difficult to get at and usually require special tools.
The mechanism used to raise and lower the paddle, is typically a servo motor located above the supporting rods, but below the paddle. In these systems, the paddle is driven into the furnace to its final position and then lowered by use of the Servo motor. When it comes time to remove the boats, the process is repeated. This system is unduly complicated in that it requires an additional motor and controlling system. In addition, when the boats rest on the tube in the furnace, it is quite common for these boats to stick slightly. When the servo motor lifts the paddle up, there is a sudden release of energy in the vertical direction when the boat becomes unstuck from the furnace tube. This sudden release of energy can damage the silicon wafers and even in some cases, knock them out of their resting position in the boat.